The present invention relates generally to spargers and more particularly to a sparger and method for adding pure oxygen or relatively high concentrations of oxygen directly into a fluid bed reactor.
Significant economic advantages can be realized by using pure oxygen instead of air to form acrylonitrile via propane ammoxidation. The ammoxidation process typically consists of reacting propane, ammonia, and air in a fluid bed ammoxidation reactor containing a suitable ammoxidation catalyst to produce acrylonitrile. Also produced are high concentrations of unreacted starting materials, for example, unreacted hydrocarbons and other remaining flammable reactants. These unreacted materials are typically recycled, that is, mixed, in a recycle stream leading back to the fluid bed reactor.
Delivery of an oxygen feed comprising oxygen or high concentrations of oxygen into the fluid bed reactor is challenging because of the sensitivity of working with pure oxygen or oxygen-rich streams. By using an oxygen feed instead of an air feed, flammability envelopes are widened and oxidation reactions are accelerated.
Typically, one or more spargers are incorporated into the fluid bed reactor vessel for delivering into the interior thereof and agitating therein the reactants of the ammoxidation process. During a propane ammoxidation process, temperatures may vary within the reactor vessel from about 400 to 500xc2x0 C. and, accordingly, spargers disposed within the reactor vessel will likewise vary in temperature as will the reactants carried by the sparger. As the temperature of a conventional sparger increases with increased reactor temperature, the flammability of a combustible material in the presence of an oxygen feed delivered therethrough would increase. As a consequence, spargers could exhibit undesirable burning because of their increased likelihood to ignite within the widened oxygen flammability limits. For example, spargers made of ordinary metals like carbon steels or even stainless steels, if used to inject pure oxygen or relatively high concentrations of oxygen, may ignite and locally burn inside a fluid bed reactor vessel for propane ammoxidation.
The present invention provides a sparger and method for injecting an oxygen feed into a fluid bed reactor. The sparger and method have particular application for injecting an oxygen feed into a fluid bed catalytic reactor for the ammoxidation of a propane feed and an ammonia feed. The oxygen feed may be oxygen enriched air (greater than 21% oxygen), pure oxygen (100% oxygen) or a high concentration of oxygen (greater than 50% oxygen). Other representative processes in which principles of the instant invention may be employed are the catalytic cracking of oils to produce gasoline and other light hydrocarbons, the coking of residua, coke gasification, the oxidation of benzene or n-butane or maleic anhydride, the ammoxidation of propylene to acrylonitrile, and the oxidation of hydrogen chloride to chlorine.
According to one aspect of the invention, the sparger and method are characterized by a feed conduit for conducting the oxygen feed and a nozzle connected to the feed conduit for passage of the oxygen feed from the feed conduit to outside the sparger. The nozzle includes an orifice and a shroud, and insulation surrounds the conduit and also surrounds the shroud substantially the full length of the shroud. In a preferred embodiment, a conduit jacket surrounds the conduit and a shroud jacket surrounds the shroud, and insulation is interposed between the conduit and conduit jacket and between the shroud and he shroud jacket. Also in a preferred embodiment, the shroud jacket terminates at a cheek plate at least partially closing an outer end of an annular space between the shroud and shroud jacket, which cheek plate closely surrounds the shroud but is radially spaced apart from the shroud by an amount sufficient to allow for differential expansion.
According to another aspect of the invention, a fluid bed reactor comprises a reactor vessel for containing a fluid bed and a sparger disposed within the reactor vessel for delivery of an oxygen feed into the fluid bed. The sparger includes at least one nozzle for directing a stream of the oxygen feed into the fluid bed. The nozzle is at least partially thermally insulated for inhibiting heat transfer from the interior of the reactor to the interior of the nozzle in order to maintain, at a fluid bed temperature greater than about 400xc2x0 C., the temperature of the oxygen feed below a temperature at which the materials of construction of the nozzle (or any combustible impurities therein) would ignite.
According to yet another aspect of the invention, a method is provided for introducing an oxygen feed into a fluid maintained at a temperature of about 400xc2x0 C. or higher, the method comprising the use of a sparger disposed within the fluid bed for introducing the oxygen feed into the fluid bed through at least one sparger nozzle.
According to a further aspect of the invention, a method is provided for the production of acrylonitrile via propane ammoxidation comprising the steps of introducing propane and ammonia into a fluid bed reactor, introducing an oxygen feed into the fluid bed reactor through a sparger to react the propane, ammonia and oxygen feed in the presence of a fluid bed catalyst to produce the corresponding acrylonitrile, and maintaining the temperature of the oxygen feed while inside the sparger below the temperature at which the materials of construction of the sparger (or any combustible impurities therein) would ignite.
The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail one or more illustrative embodiments of the invention, such being indicative, however, of but one or a few of the various ways in which the principles of the invention may be employed.